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Post subject: Hot rod Deluxe repair anomaly
Posted: Tue Feb 26, 2013 12:21 pm
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So i got this amp on the bench and the problem was the 470ohm 5watts that are always suspect. Upon replacement amp works great EXCEPT....... Ready for this.....??????

The Diodes that are in that section, I think they are 5353's, 2 or em. Unsolder themselves from the board every time the amp is on longer than 3 minutes. It literally heats up hot enough to melt solder in seconds. I haven't checked voltages but I did remove the diodes and checked with meter. They are still oneway streets. Wondering what might be causing this problem. Excessive current/voltage? Faulty part?????

Any thoughts on this???
Thank you


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Post subject: Re: Hot rod Deluxe repair anomaly
Posted: Tue Feb 26, 2013 5:15 pm
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You talk about diodes on pin 3 of the 6L6 ?

You said the reading ( ohm with meter )of these diodes are ok : On direction only ?


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Post subject: Re: Hot rod Deluxe repair anomaly
Posted: Tue Feb 26, 2013 6:23 pm
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Sorry I will be more specific. I changed the two 470ohm resistors (R78,R79) as these are usually the culprit in the supply voltage for the relays and such. When I changed them it took care of my problem, which was a "quiet" clean channel. I then noticed that the diodes 1N5353B (CR13, CR14) were not seated and looked like they had bad solder joints. Reflowed them and flipped her on. Traces started to burn up on those diodes and release the magic smoke. I watched the solder on the pads flow and the diodes dropped right out of the pads. I am going to take some voltage measurements tonight from Xfmr to C40 and C41 and see if there is a problem in there.
I have never seen heat in a relatively low voltage area as this get hot enough to flow solder????????????


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Post subject: Re: Hot rod Deluxe repair anomaly
Posted: Tue Feb 26, 2013 6:24 pm
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And, yes the diodes checked low resistance one way and OL the other on my DMM in continuity/Diode check setting.


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Post subject: Re: Hot rod Deluxe repair anomaly
Posted: Tue Feb 26, 2013 9:21 pm
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Measure the resistance of R78 and R79. Is it possible that those two resistors are 47 ohms instead of 470 ohms? Did you reattach the green ground wire from the board to chassis?

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Hot rod Deluxe repair anomaly
Posted: Wed Feb 27, 2013 2:21 am
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goldstache wrote:
And, yes the diodes checked low resistance one way and OL the other on my DMM in continuity/Diode check setting.


Shimmilou have good point ; check resistors FIRST.
____________________________________________________
Chance diodes are OK with these reading, If DMM is right. Better to check voltage on diode with amp power ON. These are Zener diodes, you must have 16 DC volts. DMM probe each side of diode.

Be sure the the copper trace are in good shape , not broken or too small, put some more solder or wire if needed . Look like diodes have not good contact with copper trace .The holes where they are could have a broken copper trace. Or wrong resistor value.

Those 5 watts are better to not seat tight on the board ; must evacuate the heat.

I hope you can understand my poor english , I'm french Canadian


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Post subject: Re: Hot rod Deluxe repair anomaly
Posted: Sat Mar 02, 2013 1:30 am
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sorry I couldn't reply sooner. Alas, I found the problem! I was just going over the amp in a general way. Checking tube socket tension, speaker nuts, that kinda stuff. Sure enough I dusted off the board with a brush to remove surface gunk, Fired it Up, and voila'! Fixed. Took another look at the board and there was a small lead from a resistor that had bent and was sending voltage around the 470 ohm resistors in the relay section! That's how much stress those resistors are under in this amp, and probably why they go faulty so frequently.

Thanks for the awesome advice and your courtesy.
Now lets warm up some bottles!


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